HARARE, Zimbabwe — When Robert Mugabe stepped down as president this week, Mevion Gambiza, 28, quickly joined the throng of people celebrating the sudden end of his 37-year rule. Mr. Gambiza jumped on the roof of a taxi and rode around as the driver honked through the streets of the capital.

But by Friday morning, Mr. Gambiza, like many other Zimbabweans, had sobered up. By the time he came to the National Sport Stadium to watch the swearing-in of the new president — Emmerson Mnangagwa, Mr. Mugabe’s longtime right-hand man — it was more to witness history than from any enthusiasm.

“Nothing will change; poverty and suffering will continue,” said Mr. Gambiza, a graduate of the University of Zimbabwe. The only difference now, he said, was that one faction of the governing party had “outcompeted its rival, and now Mnangagwa’s bootlickers will have their full turn to loot from the state coffers.”

Mr. Mnangagwa, who fled into a brief exile after losing a power struggle less than three weeks ago, became Zimbabwe’s new president on Friday, succeeding Mr. Mugabe, 93, the leader he had backed for decades before helping to oust him last week.

It was a rapid reversal of fortunes that abruptly ended Mr. Mugabe’s rule — one of the longest reigns in Africa’s post-colonial history — and set off a complex mix of exhilaration, hope and deep skepticism among Zimbabweans.

In his address, Mr. Mnangagwa (pronounced muh-nahn-GAHG-wah) said that the country’s domestic politics had “become poisoned and rancorous and polarizing,” apparently referring to the factional fighting inside the governing party, ZANU-PF.

“We should never remain hostages of our past,” Mr. Mnangagwa said, adding that his compatriots should “let bygones be bygones, readily embracing each other in defining a new destiny in our beloved Zimbabwe.”

The tens of thousands present in the stadium — most of them ZANU-PF die-hards who had been bused into the capital, Harare, from distant towns and villages in the party’s rural strongholds — loudly cheered Mr. Mnangagwa and hailed him as a “hero” and “liberator.”

Emerson Zinyera, 54, a retired police officer, said: “Today is true independence day. The one that was there was false. Today is independence that everyone, every Zimbabwean, can enjoy, not independence enjoyed by two people, Mugabe and his wife, Grace.”

But even as Mr. Mnangagwa promised a new era of democracy, the new leader, who was long known as Mr. Mugabe’s ruthless enforcer, faced a far more doubtful nation.

“This is a happy day,” said Virginia Kamoto, 34, a ZANU-PF member who was bused in with other supporters from southern Zimbabwe. “I was personally tired of Mugabe, who had stayed for far too long in power. I hope President Mnangagwa will not overstay in power. I hope he will not repress the people or tolerate corruption so that our country will be counted among the great nations of the world.”

Mr. Mnangagwa’s exact role in the military intervention that led to Mr. Mugabe’s downfall is not yet known. But on Wednesday, just hours after returning to Zimbabwe from South Africa, Mr. Mnangagwa thanked the generals who had backed him, saying he had been “in constant contact with the service chiefs throughout” the recent events.

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After nearly four decades in power, Zimbabwe's ruler, Robert Mugabe, resigned in the wake of a military takeover. How did the notorious strongman manage to keep his opponents at bay for so long?Published OnNov. 21, 2017CreditImage by Jekesai Njikizana/Agence France-Presse — Getty Images

The victory of Mr. Mnangagwa and the military — over a ZANU-PF faction led by Mr. Mugabe’s 52-year-old wife, Grace, and younger politicians with no experience in the nation’s war of liberation — underscored the old guard’s enduring grip on power, not only in Zimbabwe but also in nations like Angola, Mozambique, Namibia and South Africa.

In all those countries, former liberation movements have held uninterrupted power over decades through a combination of patronage, coercion and, in some cases, outright military force.

In his 37-minute speech, Mr. Mnangagwa emphasized rebuilding the country’s economy by, in part, re-engaging with Western nations that cut off most ties with Zimbabwe after the seizure of white-owned farms starting in 2000. Mr. Mnangagwa said that compensation would be offered to those who had lost their properties, signaling his commitment to a process that had begun fitfully in recent years.

Mr. Mnangagwa reached out to rivals, though only in general terms. He praised the man he had helped topple by saying that “history will grant him his proper place and accord him his deserved stature as one of the founding fathers and leaders of our nation.”

“To me personally, he remains a father, mentor, comrade in arms and my leader,” he said of Mr. Mugabe, who did not attend the inauguration.

But whether his conciliatory words translate to action remains to be seen. Local and international organizations have said that several leaders of the losing faction were arrested and detained by the army, which is not authorized to do so. Some are still missing, their homes have been ransacked and their relatives beaten, human rights groups say.

For years, Mr. Mnangagwa, who served as Mr. Mugabe’s personal assistant and bodyguard during the war of liberation, had seemed a natural heir. As one of Mr. Mugabe’s top lieutenants, he has been accused of spearheading Mr. Mugabe’s most ruthless policies — including the massacre of thousands of civilians in the early 1980s, the invasion of white-owned farms in 2000 and the violent rigging of polls during the 2008 election.

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A military display at the inauguration ceremony. The victory of Mr. Mnangagwa and the military in a factional struggle underscored the old guard’s enduring grip on power.CreditMarco Longari/Agence France-Presse — Getty Images

But on Nov. 6, Mr. Mnangagwa was fired as vice president by Mr. Mugabe after losing a political battle against the faction led by Mrs. Mugabe, who had vowed to succeed her husband. Mr. Mnangagwa, who said he feared for his life, fled Zimbabwe, crossing the border into neighboring Mozambique on foot, and eventually arriving in South Africa.

Then, last week, the army put the Mugabes under house arrest after the former president attempted to arrest Mr. Mnangagwa’s close ally, Gen. Constantino Chiwenga, Zimbabwe’s top military commander. Mr. Mnangagwa’s military allies, as well as his supporters inside the party, quickly maneuvered Mr. Mugabe out of power.

In Africa Unity Square, the capital’s main public area, thousands celebrated Mr. Mugabe’s resignation on Tuesday, partying late into the evening. On Friday, a few hours after the new president’s address, the mood was subdued.

“I was at Africa Unity Square on Tuesday celebrating when news broke out that Mugabe had resigned,” he said. “But I’m sure really there is nothing much to celebrate because this is just another ZANU-PF person coming to lead us, and really not much change will come from him.”

Artwell Mugari, 44, a security guard at a nearby hotel, said that on Tuesday he was caught up in the moment and found himself celebrating with the crowds pouring into the square.

By Friday afternoon, though, his mood had changed. With a younger and stronger leader, ZANU-PF had now been reinvigorated, not replaced, he said.

“I’m worried that the opposition may now never find another chance to rule,” Mr. Mugari said. “Mnangagwa was Mugabe’s right-hand man who did all the dirty work for him at every election. He knows the tricks of keeping power.”

A version of this article appears in print on , on Page A6 of the New York edition with the headline: Hopes Idle in Zimbabwe Over a Troubling Familiarity With Its Brand-New Leader. Order Reprints | Today’s Paper | Subscribe